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New Scientist Live

Squeeze light to teleport quantum energy

By Katia Moskvitch

Putting the squeeze on light may be the key to teleporting energy across vast distances. Although the amount of energy that could theoretically be transmitted is tiny for now, it could be enough to power quantum computers that don’t overheat.

For years physicists have been smashing distance records for quantum teleportation, which exploits quantum entanglement to send encrypted information. Entangled particles remain linked no matter how far apart they are, and a change to one particle always affects its partner in a particular way. In experiments, for example, a pair of entangled particles is separated and each partner is sent to a different location. When someone measures the particle at point A, its quantum state is decided and that event immediately causes a corresponding change in the particle at point B.

No physical matter is transmitted, and nothing is travelling faster than light. But the person at point B can recreate the photon at point A using only information about the observed changes – effectively teleporting the photon.

Physicists have done this with light and with matter, such as entangled ions. But Masahiro Hotta of Tohoku University in Sendai, Japan, wondered if it would be possible to also teleport quantum energy.

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Quantum toothpaste

Theory has it that a vacuum is not truly empty – it is constantly roiling with tiny fluctuations that cause particles to pop in and out of existence. These particles pop up in entangled pairs and, crucially, the two partners can appear great distances apart.

The quantum field in the vacuum of space is usually at its lowest energy level. But if someone measures the field, the quantum system in that region – let’s call it region A – is disturbed and becomes excited, gaining energy. Hotta suggests using the information gained from that measurement to create an electric current that is tuned to the quantum change. Because particles spread across the vacuum are entangled with each other, sending the current through another part of the vacuum – region B – will allow the current to extract energy from the quantum field in that region. In other words, particles from region A will teleport some of their energy to region B, without the need for a physical transmission line.

“A measurement made at point A provides the information needed to unlock hidden energy at point B,” says Seth Lloyd, a physicist at the Massachusetts Institute of Technology, who was not involved in the research. But Hotta’s original theory suggested energy teleportation would work only over a few tens of nanometres.

Light work

To get greater reach, Hotta and his colleagues have now applied a twist to their theory that adds squeezed light to the vacuum. In quantum mechanics, there is a limit to how precisely we can know multiple values in a physical system. Physicists can exploit this effect by increasing the uncertainty of one value on purpose, allowing them to better pin down a different target property.

“Like toothpaste, if you make the tube smaller in one part, it gets bigger in another direction,” says William Unruh at the University of British Columbia in Vancouver, Canada, who did not take part in the study.

Normally, photons travelling through a vacuum arrive randomly. Reducing uncertainty in the light’s amplitude, which is proportional to the number of photons travelling together, forces more of its photons to travel in pairs. When this squeezed light is sent through the space between two targeted regions, it enhances the entanglement between those regions, so that energy can be extracted across greater distances, says Hotta.

Cooler computing

Entanglement is also fundamental to quantum computers, which promise faster processing speeds by replacing binary 1s and 0s, used to store information in standard computers, with qubits that can be both 1 and 0 simultaneously. But even qubits need a power source to operate, and right now that comes from electrical current running through a quantum chip, which gives off waste heat as it travels that can destroy the fragile state of entanglement. By replacing electrical wiring with teleported quantum energy, qubits could safely maintain their entanglement, says Hotta.

The amount of energy teleported would still be very small – about several hundred microelectronvolts – so even though it should work over greater distances, it is more likely that Hotta’s teleportation technique will only be useful for now in quantum chips that send energy over a few hundred micrometres.

In principle, though, quantum energy teleportation could one day be useful to much larger machines, says Lloyd&colon; “While it currently seems unlikely that one could power a spaceship, or even a desk light, by quantum energy teleportation, you never know.”